1. Field of the Invention
The present invention relates to a dielectric actuator.
2. Description of the Related Art
When a high voltage is applied between a pair of electrodes with an elastic insulating material interposed the pair of electrodes, the elastic insulating material is polarized. Positive charge is accumulated in one of electrode surfaces opposed to each other and negative charge is accumulated in the other electrode surface. Since the electrodes attract one another due to a coulomb force acting between the charges, the elastic insulating material is crushed, and force and displacement occur extending in a direction of the electrode surface. Examples of dielectric actuators using such a phenomenon are described in Patent Documents 1 and 2.
In addition, Patent Documents 3 to 5 disclose the inventions relating to the present invention.
Patent Document 1: JP-T-2005-527178, claim 47
Patent Document 2: JP-A-2006-82346
Patent document 3: JP-UM-A-3-028767
Patent Document 4: JP-A-10-150234
Patent Document 5: JP-A-2007-103722
The present inventors have conducted intensive study to achieve an improvement in the force and displacement amount of the dielectric actuators having the above configuration. The higher the dielectric constant of an elastic insulating material and the smaller the distance between electrodes, the larger the amount of charge in an electrode surface. Accordingly, it is thought that the force and displacement amount of the dielectric actuators increase due to the increasing Coulomb attraction. From this viewpoint, first, the present inventors have studied using an elastic insulating material having an excellent insulating property and an excellent dielectric constant and reducing the distance between electrodes, as in the technique proposed in Patent Document 1 (see Paragraph number 0043 to 0045 in the same document).
In general, a dielectric elastic body of a high dielectric constant has a low insulating property. Thus, it is necessary to thicken an elastic insulating material in order to ensure the insulating property and the distance between electrodes thus increases, causing an antinomic problem.
A synthetic rubber is considered as a current applicable elastic insulating material for the dielectric actuators having the above configuration. Examples of the synthetic rubber include a silicone rubber, an acrylic rubber, an acryl-silicon copolymer rubber, a polyurethane rubber, a styrene-butadiene rubber, a chloroprene rubber, chlorosulfonated polyethylene, a nitrile rubber and the like. However, such rubber materials themselves do not have a high dielectric constant.
The present inventors thought of employing an unprecedented new method, in which an elastic material having a high dielectric constant with a poor insulating property and an elastic material having an excellent insulating property with a comparatively low dielectric constant are superimposed in layers, to solve the problem. That is, an elastic, high-dielectric material having a poor insulating property but having a high dielectric constant is obtained by mixing a conductive filler such as carbon in a synthetic rubber. The elastic, high-dielectric material is interposed between elastic insulating materials, having an excellent insulating property, in which a conductive filler is not mixed. After that, when a dielectric body in which the elastic, high-dielectric material is interposed between the elastic insulating materials is inserted between electrodes, a phenomenon is recognized in which a displacement amount with respect to an applied voltage is increased despite the increasing distance between the electrodes and the resulting reduced coulomb force (see FIG. 4 of Example).